The subject invention relates to electric induction furnaces for heat treating a running length of metal, such as steel or aluminum, and more particularly, to an improved assembly facilitating a greater convenience of coil movement on and off of the continuous strip.
Heating of a continuous strip with an induction furnace is well known. Commonly assigned U.S. Pat. No. 4,761,530 shows such an assembly. To the extent that the teachings of this patent can clarify or supplement the disclosure of the subject invention in this application, it is hereby incorporated by reference. Such heating assemblies have particular application in galvanizing or galvannealing operations, and the workpiece being treated is usually a running continuous strip of metal. Practical problems with such an operation concern the separation or removal of the furnace coils from about the strip without cutting the strip, or disassembling the heating apparatus. The ""530 patent noted above discloses one way of avoiding cutting or disassembly is to construct the coil to have a sidewall segment comprised of a hinged door, which door may be selectively opened or closed by a piston and cylinder actuator. When the door is closed, the coil is formed into a closed loop and can function as a normal solenoidal coil about the workpiece. When the door is opened, the loop has an open segment which will allow the coil to be moved off the strip for adjustment, maintenance or the like. The coil can also be moved back onto the strip, and then the door closed to form the closed loop and resume the intended heating operation. The ""530 patent shows a wheeled carriage assembly which supports the coil and facilitates the translation of the coil on or away from the strip when the coil door is opened.
There are two particular problems in the design of a furnace for this intended purpose. First, a running strip is a very dangerous item particularly for coolant hoses and electrical cables in that any contact with the running strip will result in a sawing action that can quickly cut the contacting item. Accordingly, the furnace design must be very careful to space the furnace components to avoid any such contact. An even better solution is to minimize the need for coolant hoses or electrical cables, particularly in the area of the strip.
The other problem is that in most induction coil applications, the current in the load coil is higher than other power components and the current is largely reactive. As such, it is advantageous to supply the reactive portion of the coil current from a capacitor bank located as close as possible to the induction coil to minimize the losses between the bank and the coil. Apart from the cable connecting problems mentioned above, the proximity to the coil enhances the consequences of the field effects of the coil on the bank. When such effects can cause an unacceptable heating of the bank, the prior art suggests spacing the bank away from the coil.
Another problem with the system shown in the ""530 patent above apart from the complexity itself with a hinged door, is that the nature of the high frequency currents in such an assembly are that they run on the inside surfaces of the coil. In the switch assembly of the ""530 patent the switch blades are disposed so that the current, instead of running down the wide part of the knife blade, actually runs down the edge of the knife. It is better that the switch can emulate a piece of bus bar, i.e., by providing a surface area greater than the knife edge, the more efficient and the lower the losses will be, for the connection.
The present invention contemplates a new and improved apparatus which overcomes all of the above-referred to problems and others to provide a new induction heating assembly for preferably heating a running strip which is simple in design, economical to manufacture, readily adaptable to a variety of dimensional characteristics, is rugged and reliable in its operation, provides improved heating efficiency, increased reliability and reduced assembly cost.
In accordance with the present invention, there is provided an electric induction heating assembly comprising an induction coil for heating a workpiece passing therethrough and a capacitor bank for supplying a reactive portion of current to the coil wherein the bank is disposed adjacent the coil and includes a housing configured for shielding capacitors within the bank from a magnetic field of the coil. The bank is preferably fastened to the coil and includes a conduit in communication with a source of coolant for cooling the banks.
In accordance with another aspect of the present invention, the housing comprises an electrically and thermally conductive heat sink, and the bank comprises a plurality of capacitors, each configured as a toroidal roll pack disposed between a first and second of the heat sink. A collector bus is in electrical communication with the capacitors and the coil. In one embodiment a plurality of the roll packs are serially connected to the bus and each of the roll packs is interposed between a pair of the plurality of heat sinks for forming a stack.
In accordance with another aspect of the present invention, the coil includes a selectively openable switch and an actuator for deforming the coil to open the switch with a spacing sized for moving the assembly on and off of a running strip. A moveable carriage supports the coil and the capacitor bank.
In accordance with the present invention, an induction heater is provided for heating a continuous strip wherein the heater is selectively moved on and off the strip. The heater comprises a closed loop coil disposed about the strip. An accessway is included within the coil for selectively opening the coil for the movement relative to the strip. The accessway comprises a switch supported by a turn of the coil. An actuator is associated with the turn for deflecting the turn to an extent to open the switch.
In accordance with another aspect of the present invention, the switch comprises a knife switch extending for a length of the coil. The actuator preferably comprises a piston and cylinder assembly supported on a base frame and fastened to the coil for the deflecting of the coil turn.
In accordance with another aspect of the present invention, the heater includes a flat pack capacitor bank in electrical communication with the coil. The bank and the coil are supported on a trolley for movement on and off the strip.
One benefit obtained by use of the present invention is an induction heating assembly comprising a carriage mounted coil wherein the coil and an associated capacitor bank are packaged in the assembly for reduced space consumption.
Another benefit is an assembly with a reduced number of coolant hoses and cable connections adjacent the coil and a running strip passing through the coil.
Another benefit is an openable coil including a knife switch wherein the coil has the advantages of lower losses, increased reliability, less sensitivity to alignment, lower switch costs, and which avoids end water and cooling hose connections.
Yet another advantage of the present invention is a flat pack capacitor pack which can be bolted directly to the coil, but which avoids harmful heating of the capacitor bank by appropriate shielding and cooling.
Another benefits and advantages of the subject new induction heating assembly will become apparent to those skilled in the art upon a reading and understanding of this specification.